It is well known that protein drugs suffer from the problem of denaturation caused by heat, organic solvents and/or unfavorable pH (Weiqi Lu et al., PDA J. Pharm. Sci. Tech., 49, 13-19 (1995)). They are usually administered by injection; however, because their in vivo activities last only for a short period of time after administration, they have to be administered repeatedly when a long-term treatment is required. For example, to treat a pituitary deficient child's dwarfism, human growth hormone (hGH) must be injected daily or every other day for a period of 6 months or more. Therefore, there have been many efforts to develop effective sustained-release formulations of protein drugs.
For example, extensive studies have been made to develop a sustained-release microparticle formulation prepared by coating a protein drug with a synthetic biodegradable polymer, e.g., polylactide, polyglycolide, poly (lactide-co-glycolide), poly-ortho-ester or polyanhydride, which continuously releases the drug or the antigen as the polymer degrades in the body (M. Chasm and R. Langer, ed., Biodegradable Polymers as Drug Delivery Systems, Marcel Dekker (1990); and Heller, J., Adv. Drug Del. Rev., 10, 163 (1993)). Although this type of formulation has several advantages, it suffers from the serious problem that the drug undergoes denaturation upon to its contact with an organic solvent during the preparation process thereof (Park, T. G. et al., J. Control. Rel., 33, 211-223 (1995)). The use of an organic solvent is unavoidable because a biodegradable polymer dissolves only in an organic solvent, e.g., methylene chloride, ethyl acetate, acetonitrile, chloroform or acetone.
In order to avoid such undesirable contact of a drug with an organic solvent, Lee et al. have prepared a microparticle by coating an protein with a water-soluble polymer to obtain a primary particle; dispersing the primary particle in an organic solvent containing a biodegradable polymer; and drying the resulting dispersion to obtain a final microparticle (Lee H. K. et al., J. Control. Rel., 44, 283-294 (1997); and U.S. Pat. No. 5,753,234). However, the process of preparing such microparticle is complicated and uneconomical.
There have also been attempts to develop a sustained release formulation containing a natural polymer, e.g., gelatin, collagen, chitosan, carboxymethyl cellulose, alginate or hyaluronic acid. The natural polymer easily absorbs water to form a gel having a high viscosity which releases a drug or antigen slowly. For example, U.S. Pat. No. 5,416,017 discloses a sustained-release injection formulation of erythropoietin containing a 0.01 to 3% hyaluronic acid gel; Japanese Patent Laid-open No. 1-287041 (1989), a sustained-release injection formulation of insulin containing a 1% hyaluronic acid gel; Japanese Patent Laid-open No. 2-213 (1990), a sustained-release formulation of calcitonin, or human growth hormone containing a 5% hyaluronic acid gel; and Meyer, J. et al. (J. Controlled Rel., 35, 67 (1995)), a sustained release formulation of granulocyte-colony stimulating factor (G-CSF) containing a 0.5 to 4% hyaluronic acid gel.
Such hyaluronic acid gel formulations have a sustained release effect because the protein drugs slowly pass through the gel matrix having a high viscosity. However, a gel having a hyaluronic acid concentration of several % has a high viscosity, e.g., in the order of 105 to 107 centipoise, which makes the injection thereof difficult. Further, since both the drug and hyaluronic acid dissolve in water, a hyaluronic formulation is easily diluted by the body fluid after injections with a consequential rapid release of the drug, usually within a day. For example, Japanese Patent Laid-open No. 1-287041 (1989) discloses that when a 1% hyaluronic acid gel formulation containing insulin was injected to a rabbit, the effect of lowering the blood glucose level was sustained for only 24 hours; and Meyer, J. et al. (vide supra) and U.S. Pat. No. 5,416,017, that when a 2% hyaluronic acid gel formulation containing G-CSF and a 1.5% hyaluronic acid gel formulation containing interferon-a, together with serum protein are administered to an animal, blood levels of these protein drugs suddenly drop to below 1/10 of the initial levels in 24 hours.
Benzyl hyaluronate (HYAFF™, Fidia S.P.A.), a synthetic ester prepared by esterifying natural hyaluronic acid with benzyl alcohol, does not dissolve in water but in an organic solvent such as dimethyl sulfoxide (DMSO). A solid benzyl hyaluronate microparticle formulation containing a protein drug has been prepared by the emulsion-solvent extraction method (Nightlinger, N. S. et al., Proceed. Intern. Symp. Control Rel. Bioact. Mater., 22nd, Paper No., 3205 (1995); and Ilum, L. et al., J. Controlled Rel., 29, 133 (1994)), which is conducted by dissolving benzyl hyaluronate in DMSO; dispersing the protein drug in the resulting solution; adding the resulting dispersion to mineral oil to form an emulsion; and adding a solvent which is miscible with DMSO, e.g., ethyl acetate, to the emulsion to extract DMSO therefrom to obtain solid microparticles comprising the protein drug and benzyl hyaluronate.
However, the benzyl hyaluronate formulation has the drawback that the protein drug can be easily denatured by the organic solvent used in the preparative step and also by hydrophobic benzyl hyaluronate itself. An in vitro release test of a benzyl hyaluronate microparticle comprising granulocyte macrophage-colony stimulating factor (GM-CSF) showed that only 25% of GM-CSF was released in the initial 2 days, and no more of GM-CSF, thereafter (Nightlinger, N. S. et al., vide supra), suggesting that most of the protein drug was denatured.
Accordingly, it is an object of the present invention to provide a microparticle having an improved stability and effective delivery of a drug.
In particular, it is an object of the present invention to provide a sustained-release drug formulation where the active ingredient is a peptide or protein drug.
It is another object to provide a procedure for formulating a peptide or protein drug into an injectable product while avoiding significant denaturation of the drug.
It is yet another object of this invention to provide method of producing an injectable formulation of a peptide or protein drug by spray drying a mixture containing the drug.